1. Field of the Invention
The present invention relates to a liquid-drop discharge device used in various machineries for processing liquid by performing discharge of the liquid, and more particularly to liquid drop discharge devices performing spraying operations in an operating environment in which the internal pressure of a reaction cell is lower than the internal pressure of a liquid storage tank or a liquid reservoir.
2. Description of the Prior Art
Ink jet discharge devices as disclosed, for instance, in Japanese Patent Unexamined Publication No. 6-40030 (1994) are conventionally known types of devices for discharging liquid in the form of minute particles used in particular fields. However, such discharge devices are used in offices or schools under relatively stationary conditions with little fluctuations in the temperature or pressure of peripheral environments when being used, and are not exposed to significant fluctuations in operating environments.
On the other hand, minute powder forms of various chemicals are being used as auxiliary products in the manufacturing of semiconductors or the like, wherein required standards in view of particle size can not be achieved by simply using mechanical crushing means. It would, therefore, be desirable to develop new manufacturing methods for new types of chemical powders. In one exemplary method for supplying raw materials in the form of minute particles to substrates in reaction cells, it is a strict requirement to supply the chemical powder particles into drying chambers in a stable manner. It is thus highly desirable to develop devices that may be used with such methods for discharging liquid as particles ranging from several hundreds of nanometers to several tens of microns in a stable and controlled manner. Fluctuations in operating conditions produce remarkable variations in the environments of discharge spaces, and it is presently the case that no device has yet been proposed with which supply liquid can be discharged as minute particles in a desirable manner in the presence of these variations in discharge space environments.
The present invention has been made with the aim of providing a liquid discharge device for discharging raw materials or the like. The liquid discharge device being arranged to continuously adjust a condition for discharging liquid to be an optimal condition even when environmental conditions of peripheral environments fluctuate or vary, and for stably discharging liquid even though the operating environment may be one in which the discharge space is prone to abrupt and accidental fluctuations in operating conditions.
For solving the above problems in the prior art, the inventors have devised a liquid-drop discharge device made up of a plurality of liquid-drop discharge units each of which include a liquid discharge nozzle for discharging liquid supplied from a liquid storage tank, a pressurizing chamber for pressuring liquid to be discharged through the nozzle, an introducing hole for supplying liquid to the pressurizing chamber from the storage tank, and a piezoelectric/electrostrictive element for causing pressurizing operations. The liquid-drop discharge device further includes a liquid discharge means in which respective liquid introducing holes of adjoining liquid-drop discharge units are connected to a common liquid supply path, and a reaction cell provided having a space into which the nozzles face for discharging liquid from the discharge units. An internal pressure of the liquid storage tank (P1) and an internal pressure of the reaction cell (P3) have the following relationship: P1 greater than P3. With this arrangement, since the internal pressure of the reaction cell (P3) is a negative pressure with respect to the liquid storage tank (P1), drops of discharge liquid can be effectively discharged through the liquid introducing holes of the adjoining liquid-drop discharge units owing to the driving force of the positive pressure of the pressurizing chamber to thereby enable sufficient spraying of large amounts of liquid.
It should be noted that for the purpose of appropriately performing spraying operations in situations where the internal pressure of a reaction cell is lower than the internal pressure of a liquid storage tank, or that of a liquid reservoir, a known method exists wherein spraying is not directly performed from a spraying outlet of a liquid storage chamber to the reaction cell but wherein a separate pressurizing chamber is provided between the spraying outlet and the reaction cell for adjusting the internal pressure of the pressurizing chamber to be equal to that of the internal pressure of the liquid storage chamber, and then performing spraying operations from the spraying outlet to the reaction cell through the pressurizing chamber. This method, however, does not provide a liquid discharge device capable of spraying large amounts of discharge liquid.
Another aspect of the invention relates to a liquid-drop discharge device which includes a liquid storage tank, a liquid reservoir having a specified capacity that is connected to the liquid storage tank by means of a check valve, a liquid discharge means for discharging liquid from the liquid reservoir, and a reaction cell provided to have a space into which liquid is discharged from the liquid discharge means. The liquid discharge means includes a plurality of adjoining liquid-drop discharge units respectively connected to a liquid supply path communicating with the liquid reservoir. Each of the liquid-drop discharge units includes a liquid discharge nozzle facing the reaction cell to discharge liquid from the discharge units, a pressurizing chamber for pressurizing liquid to be discharged through the nozzle into the reaction cell, an introducing hole for supplying liquid from the liquid supply path to the pressurizing chamber, and a piezoelectric/electrostrictive element for causing pressurizing operations. A differential regulating tube is provided between the liquid reservoir and the reaction cell to connect the reservoir and reaction cell to one another, and maintains a specified relationship between an internal pressure of the liquid reservoir and an internal pressure of the reaction cell. The differential regulating tube is controlled such that the above-discussed internal pressures satisfy the following relationship: P1xe2x89xa7P2xe2x89xa7P3; wherein P1, P2 and P3 respectively represent an internal pressure of the liquid storage tank, the internal pressure of the liquid reservoir, and the internal pressure of the reaction cell. With this arrangement, it is possible to prevent backflow of fluid from the reaction cell to the liquid reservoir or from the liquid reservoir to the liquid storage tank.
Preferably, a float reservoir is employed in the liquid reservoir and functions to maintain a liquid surface level constant for preventing backflow of liquid to the liquid storage tank. The float reservoir also maintains a pressure at which liquid is supplied to the liquid-drop units to be constant. It is further desirable to set the internal pressure P1 of the liquid storage tank to be at an atmospheric pressure for enabling successive supply of liquid from the storage tank.
It is further desirable to control the pressure differential existing between internal pressure P2 of the liquid reservoir and the internal pressure P3 of the reaction cell to be a constant pressure differential. With this constant pressure differential arrangement, it is possible to avoid cases in which adjustments of spraying amounts cannot be performed because the pressure differential is too large, which causes leakage of liquid when utilizing the pressure differential for spraying large amounts of liquid. The above-discussed arrangement is further favorable in view of stabilizing the spraying amount.
Preferably, the internal pressure P2 of the liquid reservoir is maintained to be at a specified pressure value or to exceed the specified pressure value by using a regulating valve provided on the differential regulating tube. Alternatively, the regulating value can be provided in the liquid reservoir. With this arrangement, the regulating valve may be controlled to perform the spraying of large amounts of liquid while maintaining the internal pressure P2 of the liquid reservoir in a negative pressure condition, which thereby prevents air bubbles from adhering to inner walls of the liquid reservoir or other members of the discharge device from expanding. Control of the regulating value is performed to satisfy the following relationships: atmospheric pressurexe2x89xa7P2xe2x89xa7specified pressure valuexe2x89xa7P3.
A favorably used regulating valve may be, for instance, a leak valve arranged in such a manner that a valve body pressurizes a valve seat to close the valve body through the use of an urging member and to release the valve body from the valve seat against urging forces of the urging member when the internal pressure of the reaction cell is in a specified negative pressure condition. The regulating valve could also be a solenoid valve in which releasing and closing operations are controlled at timings based on values of the internal pressure of the reaction cell, as detected by a detector or a regulator or the like.
The regulating valve is connected to a control unit, which inputs instructions for closing or releasing the valve in accordance with control signals for driving or terminating the liquid discharge means.
When the regulating valve is mounted to the differential adjusting tube, it is possible to employ a means for outputting a control signal for closing a release valve which the control unit had released for the purpose of setting the internal pressure P3 of the reaction cell and the internal pressure P2 of the liquid reservoir to be substantially equal to increase the amount of discharged liquid-drops from the liquid discharge means. A control signal could also be output to drive the liquid discharge means at the moment P3 greater than P2 is satisfied. A control means could output a control signal to close the release valve and to drive the liquid discharge means after a specified delay in view of response of the regulating valve or response of pressure. A precise control means could be employed for first outputting a control signal for closing the release valve that is in a released condition and then outputting a control signal for driving the liquid discharge means from the control unit upon detection of a negative pressure condition within the reaction cell by using a pressure sensor.
On the other hand, when the regulating valve is mounted to the liquid reservoir, it is possible to favorably employ a control means for outputting control signals for releasing a leak valve that had been closed by the control unit for setting the internal pressure P3 of the reaction cell and the internal pressure P2 of the liquid reservoir to be substantially equal and driving the liquid discharge means either the moment P3 greater than P2 is satisfied or at a somewhat delayed timing by a specified time in view of response of the regulating valve or pressure. A control means is also preferably used to output control signals for driving the liquid discharge means in accordance with signals from the pressure sensor provided within the reaction cell.